Quantity Stock Type
Balance of all stock = Sum of IN type - Sum of Out type
E.g: Sum of IN type = 22
Sum of OUT type = 3
Balance of all stock = 22-3
I WANT THE QUERY RESULT RETURN 17
Note: When there is only STOCK IN, the query should return balance for STOCK IN .
When there is only STOCK OUT, the query should return balance for STOCK OUT.
When there is no STOCK, the query should return nil balance.
Remember the query result is only one output, which is the current stock balance. But it caters for
conditions stated in Note above.